Automatically increasing fault tolerance in distributed systems

Developing fault-tolerant distributed protocols is a difficult task. The difficulty of this task increases with the severity of the failures to be tolerated. One way to deal with this difficulty is to develop protocols tolerant of benign failures and then transform these protocols into ones that are tolerant of more severe failures. This transformation mechanism is called a translation. This dissertation considers a variety of processor failures and synchrony models. The failures studied range from simple stopping failures to arbitrary faulty behavior. The synchrony models range from systems in which processors are fully synchronized (synchronous systems) to systems in which processors are not synchronized at all (asynchronous systems). For all synchrony models, the dissertation gives general definitions of translations and of measures to evaluate their performance. The two measures considered are communication complexity and fault-tolerance. Communication complexity is the communication overhead incurred when using a translation. Fault-tolerance is the maximum proportion of processors that can be faulty without affecting the correctness of the translations. For synchronous systems, this dissertation presents a complete study of the relationship between fault-tolerance and round complexity of translations. It develops new translations that are optimal and proves that some previously developed translations are optimal. For asynchronous systems, it proves that some previously developed translations are optimal. For systems that are only partially synchronous this dissertation discusses some of the issues involved in designing efficient translations.